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Original question:

LMK00804B: Q output termination configuration

LMK00804B: Q(LMK00804B) output connected to LMX2594RHAR, Overshoot observed.

Dharmaraj karupusamy
Prodigy 230 points
Part Number: LMK00804B
Other Parts Discussed in Thread: LMX2594,

HI Team,

From LMK00804B(Q0) to LMX2594(SYNC) clocks are having some overshoot. Exceeding the accepted VIH level of LMX2594RHAR(receiver).Kindly suggest solution to overcome this. Is it  recommended to add shunt capacitor at receiver side to suppress the overshoot?

Kindly find the simulation outputs in attached file.Your valuable feedback with help us a lot.

LMK00804B Pin :
LMX2594RHAR Pin :
  • 0
    TI__Expert 5040 points

    Hello Dharmaraj,

    I'd be glad to help take a look at the overshoot you are seeing, although, the simulations attached do not seem to be attached properly.

    Please advise with attachment.

    Before we recommend a shunt capacitor we'd like to understand more of the overshoot. There shouldn't be an interfacing issue between the LMK00804B output voltage to LMX2594 input voltage. Are we using these devices at Typical voltage of 3.3V?

  • 0 in reply to Aaron Black
    Prodigy 230 points

    Hi Aaron,

    Kindly look at the sch. and simulation result and kindly advice to overcome this.

  • 0 in reply to Dharmaraj karupusamy
    TI__Expert 5040 points

    Hello Dharamaraj,

    If we are to use a bypass capacitor to reduce the overshoot you'd want to use a capacitor around 160pF to reduce signals greater than 1Ghz but for validation could you place a 1nF capacitor and simulate from there?

    Please let me know if there are other concerns or constraints due to design as the ideal case for signal integrity is to use a single board plane and it seems your board may already be designed in with vias 14+ layers. In which case, have you measured this physically and do we have physical results? I anticipate additional signal interference with via and surrounding devices.

  • 0 in reply to Aaron Black
    TI__Expert 5040 points

    Hello Dharamaraj,

    Feel free to open another E2E ticket if additional information is available. I will consider this request closed.